The present invention relates to a high-voltage (HT) power supply unit, particularly for an X-ray tube in which unit all of the high-voltage power supply functional components are contained in a single box.
X-ray tubes comprise a cathode of the filament type which emits a beam of electrons towards an anode. The anode, under the action of the beam of electrons, emits a beam of X-rays. To obtain a high-energy beam of electrons, the beam of electrons emitted by the cathode is accelerated by a strong electric field created between the cathode and the anode. To achieve this, the anode is raised to a positive potential with respect to the cathode, the potential difference between the anode and the cathode generally reaching values of 150 kV or more. These extremely high potential differences are provided by high-voltage devices.
The functional elements of these high-voltage devices are encased in an earthed metal box filled with an electrically insulating and cooling liquid.
The functional elements conventionally comprise a high-ratio HT transformer comprising primary and secondary windings, a magnetic core, HT rectifiers and HT smoothing capacitors.
More specifically, the transformer has primary windings to which AC voltages supplied by a power converter are applied, and secondary windings connected to voltage doubling rectifier circuits. The voltage doubling/rectifier circuits of each of the secondary windings are connected together so that their voltages are combined. By respecting the polarity of the rectifiers, positive or negative voltages can be added to obtain the high voltage level needed to power the X-ray tube.
The high-voltage output within the HT unit is protected by resistors connected through the HT box cover plate to hermetically sealed HT connectors, receptacles accommodating the connector pins of the HT lead connecting the HT device to the X-ray tube. The HT outputs are also connected, within the HT unit, to voltage-dividing resistors which form the upper part of a voltage divider supplying a low voltage which is proportional to the level of the output high voltage.
Also to be found within the box are the conductors needed for providing the electrical connections between the functional elements and for electrically connecting the HT power supply device to the X-ray tube.
All the functional elements need to be supported within the box and electrically insulated from one another.